This invention relates to a method of making an oilseal having a curvature section on its lip line and also a method of producing the oilseal.
Conventionally an oilseal of the above-described type has been produced through the use of a mold core which has a wavy lip line-forming plane to form a wavy lip at the time of vulcanization molding of the oilseal. For this reason, finish work on the lip line after the vulcanization molding is extremely difficult. In order to avoid the necessity of finish work on the lip line, special designing has to be made in advance for the mold core. This results in complication of the construction of the mold core and a requirement for extremely skilled workmanship.
Furthermore, the wavy lip line-forming plane of the mold core necessary to form such a wavy lip line at the time of vulcanization molding of the oilseal requires complex procedural steps. Usually, such a wavy lip line-forming plane is produced by: first, forming a pair of conical planes each of which inclines at the peripheral plane of the mold core in a direction opposite to the other, with a different inclination angle from each other and connecting to the other at a minimum diameter section, then, forming these conical planes into the wavy form.
Shaping of the wavy lip line-forming planes therefore requires high precision work and consequently production of the mold core is extremely difficult. Additionally, since the wavy lip lines of the oilseal are shaped directly by the use of the mold core, an inferior flow of rubbery material tends to occur at the wavy lip line-forming planes. This, in turn, produces defects, for example, blowholes, which cause adverse effects in sealing capability.